One of the major problems that arises in applying the top course paving of a roadway is the sealing of the joint or “seam” between pavement sections or “lanes”. Since pavement sections are applied in widths determined by the width of the paver, they are typically applied in multiple passes of the paver, with each pass loosely referred to as a “lane”. This means that there is time interval between paving one lane (referred to as the “cold joint lane”) and the next adjacent lane (referred to as the “hot joint lane”), during which time the asphalt of the preceding lane has cooled to ambient temperature. The temperature difference between the cooled pavement of the preceding lane and the fresh asphalt of the next adjacent lane makes for a weak bond between the two sections along the seam. This weakness often leads to cracking in the seam area, which allows water to penetrate into the seam and, with freezing and thawing, produces progressive deterioration and separation of the pavement sections.
Another problem that arises in the formation of seams between asphalt lanes relates to differential compaction. When an initial section of asphalt is laid, the seam end necessarily gets less compaction than the central section, because there is no vertical support on the seam end to restrain the asphalt against a compaction force. Reduced compaction in the seam area results in more voids in the asphalt, which weakens the seam and leaves it more vulnerable to moisture penetration and hence deterioration in freeze/thaw cycles.
Even when a strong bond is initially achieved in the seam between lanes, the expansion and contraction of the adjacent lanes under varying weather conditions will subject the seam to stresses and shear forces that will tend to degrade the joint over time and cause it to fail, due to the limited elasticity and tensile strength of asphalt paving materials. In effect, since it is not possible to fuse together the cold joint lane asphalt material to the hot joint lane asphalt material to create a structurally solid bond, the paving seam has to function as an “expansion joint” between adjacent lanes, since the asphalt mix typically applied in the seam area does not have the right mechanical properties to serve this function.